This invention relates to a high breakdown voltage semiconductor device having an insulated gate structure.
IGBT (Insulated Gate Bipolar Transistor) is a novel high breakdown voltage semiconductor device which is provided with a high speed switching property peculiar to a power MOSFET and with a high output property peculiar to a bipolar transistor, and hence is utilized extensively in recent years in the field of power electronics, e.g. as an inverter or a switching power source.
However, a lateral IGBT of this kind is accompanied with the following problems. Namely, at the occasion of turn-on of the IGBT, a positive voltage is applied to the gate electrode thereof thereby turning the channel region of the surface of p-type base region into a conductive state. In this case however, a voltage drop is caused to generate at this channel region to such an extent as to invite a problem that the ON-state voltage of the device becomes higher.